Treating tank for ich but unsure

[Diana]

If the white spot on the tail does not look like Ich I would not medicate for Ich.
You might check the ornaments in the tank to be sure there are no sharp things the fish can get hurt on. It seems your fish have quite a few minor scrapes.
If they are arguing among themselves, and injuring each other it may help to add more caves, or re-arrange the decor so they may find more places to settle and not fight over the best ones.

[BotiaMaximus]

I've been following along here, and would agree it seems less like Ich as more time goes by, you would have expected confirmation by now.

It seems the water changes have improved the situation quite a bit, which they should have with the high Nitrates you had.

You had said your PH was 6.4 and at one point had gone to 6.8 and that your tap water was 7. Was that correct? Are you adding something to lower PH??

** If you are lowering the PH maybe that could be a problem?

** 7.0 should be fine. I know the "specs" are 6.5 to 7.0 but mine and many others do fine in PH levels over 7.0.

** Is it possible that wounds heal slower in an acidic environment?

** = Diana Please provide correct answer

[Diana]

Many of the pH lowering products are acidic in nature and could certainly be an irritant. Do not use such products.

PH can also drop because of high levels of organic matter in the tank. As organic matter decomposes the pH drops. The organisms that do this also remove a trace amount of the minerals in a tank, which allows the pH to fluctuate more easily.
In a tank with regular water changes the tap water usually has enough minerals to replace those lost to decomposing material, and the waste material is removed so there is not very much at any one time, anyway.
In a tank where the nitrate gets too high other things (waste/organic matter) is also accumulating, and this can lead to Old Tank Syndrome, in which most or all the minerals are used up, the pH crashes to the low 6s, the nitrifying bacteria die, ammonia spikes... Bad scenario!

I have 3 examples of bacteria NOT doing so well in acidic environment, and therefore the suggestion that wounds ought to heal better because of less chance of bacterial infection. Whether this is a true link, I do not know. I am not sure how fish skin and muscle tissue regenerates with either acidic or alkaline conditions and these wounds are likely protected by slime coat as fast as the fish can produce a little extra to replace whatever was removed with the injury. The wound is not exposed directly to the water unless it is a large, deeper wound that is not covered with slime coat fast enough.
Anyway, poor bacteria growth and pH:
1) Old Tank Syndrome, dropping pH and the death of nitrifying bacteria. I am not sure if the bacteria die specifically because of the pH, or the problem is the lack of minerals. I suspect it is the pH.
I will immediately agree that nitrifying bacteria are NOT the same species that cause infections in fish.
2) Deep under peat bogs the environment is so acidic that decomposing bacteria do not live very well, if at all. Tree stumps or large branches do not decompose for many years in such a place. Again, not the same species of bacteria.
3) Fish that come from rain forest streams seem to have a less strong immune system. One conjecture for this is that the high level of tannins and low pH of this water reduces the growth of bacteria, so the fish are in less danger of certain diseases.
Fourth and widely divergent. We TAN leathers with TANNIC acid (from various sources, including oak trees) to lengthen the life of the leather, and reduce decomposing from, among other things, bacteria.